Intensification circuit for a cathode ray tube beam



J. F. SIEGEL June 20, 1961 INTENSIFICATION CIRCUIT FOR A CATHODE RAY TUBE BEAM Filed Oct. 20, 1958 E T 42 SCHMIDT TRIGGER INVENTOR. K JEROME F. SIEGEL Fig. 2

ATTORNEYS United States Patent INTENSIFICATION RAY This invention relates to an intensification circuit, and more particularly to a circuit which produces angle marker lines on a radarpresentation.

In a radar presentation of the plan position indication (PPI) type, the display is one which appears as though the observer were directly over the antenna and looking down at the earth from a great height. To produce this plan position indication, the radar antenna is capable of rotating 360, so that it covers the entire horizon. When the antenna points directly north, but sees no target, a northerly line is produced on the radar viewing screen, the line extending vertically from the center to the perimeter of the presentation. When the antenna .points directly east (or west) but sees no target, horizontal lines which radiate from the center of the presentation are produced. Thus, as the antenna changes its position, additional radial lines are produced at appropriate angles on the presentation, each line corresponding to a given antenna position. The net result is that when the antenna has gone through a complete rotation, the presentation has the appearance of a spoked wheel. While each of the radial lines corresponds to a. particular angular position of the antenna, there are so many lines that it is impractical to identify each. For this reason and others which will be later discussed, individual line designation is impracticable.

As is well known, the actual presentation is produced by bombarding a fluorescent screen with a stream of electrons. The glowing spot of light thus produced is caused to move by suitable deflection of the electron beam. The movement of the light spot which produces the radial spoke'lines of the presentation must, of course, be synchronized with the various portions of the radar system. Synchronizing signals, known as system trigger pulses are therefore cyclically produced at a very high repetition rate. These system triggers initiate, among other things, the production of the radial lines of the presentation.

When the antenna picks up a signal reflected from a target, the electron beam is intensified to produce a bright spot or blip on the presentation. The distance of the blip from the presentations center is a measure of the distance of the target from the antenna, and the position of the blip is an indication of the angular posit-ion of the target in relation to the antenna. In order to obtain the maximum contrast for the blip, the radial spoked lines of the presentation are made very dim, or may actually be blanked out entirely. This intentional blanking-out of the radial lines is another reason why the radial lines cannot be individually identified.

Whenever a target representing blip appears on the presentation, it is desirable to immediately ascertain its direction.

Since allof the radial lines are either dim or completelyblanked out, one way to ascertain direction is to intensify Onlyiselected lines of the presentation, so that they-represent particular angles. One convenient arrangementlistto have each ten degree position of the antenna indicated by an intensified spoke. In this way, as soon as a'blip'is produced, its angular position may be determined ,in. relation to the nearest marker line.

In order to produce the angle marker lines, a marker signal is obtained from the antenna at every 10 point thereof. These-marker. signals are fed to suitable cir- Patented June 20, 1961 2 cuitry, and an intensification pulse of suitable duration is produced to intensify one spoke. As previously indicated, the system trigger energizes a circuit which causes the spoke producing spot of light to move radially outward from the center. When an angle marker signal is received coincidentally with the system trigger, the intensified spoke extends from the center to the edge of the presentation. When these signals are not coincident, as is usually the case, the angle marker is only part of a spoke or complementary parts of two spokes.

It is therefore the principal object of my invention to produce an improved circuit for producing an intensification pulse for a cathode ray tube beam.

' It is another object of my invention to provide an intensifying circuit which produces single complete angle marker lines.

The attainment of these objects and others will be realized from the following specification, taken in conjunction with the drawings, in which:

FIG. 1 shows my invention; and

FIG. 2 shows the time relationship of various waveforms which occur at indicated points in my circuit.

My invention produces an angle marking line consisting of a single intensified radial line which always starts at the center of the presentation and terminates at the periphery thereof. The disclosed circuitry accomplishes this result by providing an intensification pulse which is initiated by the system trigger pulse immediately following the occurrence of a marker, and is terminated by the subsequent system trigger pulse. In this way, the intensification pulse has a duration of only the interval between adjacent system. riggers, and thus intensifies only the spoke occurring during this interval.

My invention may be readily understood from the circuit diagram of FIG. 1 and the waveforms of FIG. 2. Basically, my invention comprises an output circuit 10, such as a multivibrator, which produces the actual intensifying waveform, and an initiating circuit 12 which may also be a multivibrator, which determines when the intensifying waveform is initiated. Multivibrators 10 and 12 have the usual characteristic that only one tube thereof may be conducting at any given time.

Since the function of multivibrator 12 is to initiate the intensification pulse, the rnnltivibrator must produce an initiating signal on the occurrence of the trigger pulse following a marker signal. This result is achieved by feeding into initiating multivibrator 12 both the marker signal and trigger pulses. The operation of multivibrator 12 will be best understood by first studying its action when energized only by trigger pulses.

The output from initiating rnultivibrator 12 is obtained at anode 16 of tube 14. For convenience, multivibrator 12 will be called Off when tube 14 is not conducting. As will be hereinafter shown, multivibrator 12 is normally 011.

When only series 1% of trigger pulses is applied to multivibrator 12, it does not produce an initiating signal. This may be understood by first considering. series 18 of trigger pulses shown as waveform A in FIG. 2. In accordance with established practice, the entire series will be considered as moving to the left. Thus, the first change in level will be called the leading edge of the pulse, and it will be noted that leading edge 20 is upwardly directed, or positive going. The second change in level is called the trailing edge, and it will be seen that trailing edge 22 is downwardly directed, or negative golng.

FIG. 1 shows that system trigger waveform 18 is applied through capacitance 23 to multivibrator 12. Multivibrator 12 is preferably designed to be triggered from one state to another by sharp spike-like signals which extend above or below a reference level. In order to produce spikes capable of affecting the multivibrator, capacitance 23 acts like a diiferentiating circuit having a time constant which is of the same order of magnitude as the duration of the trigger pulse. Any differentiating circuit must of course have resistance associated therewith. In my circuit these resistances comprise the internal resistance of the tubes, the bias resistances, and the resistive portions of the feedback networks associated with multivibrators. Some of these have been omitted from the drawing in the interest of clarity, but their use and selection are well known to one skilled in the art.

In accordance with well known principles, the output from capacitance 23 is of the general shape of waveform 24 (B of FIG. 2), which is capable of causing multivibrator 12 to switch between its stable states. Waveform B is applied to grid 25 of tube 14. When a positive going pip, resulting from the positive going leading edge of pulse 28, is applied to control grid tube 14 becomes conductive, thus turning multivibrator 12 On. Whcn a negative going pip resulting from the subsequent negative going trailing edge 22 of pulse 18 is applied to grid 25 of tube 14, the tube is cut off. Thus, multivibrator 12, which is normally Off, is turned On periodically and for extremely short intervals by the individual pulses of system trigger waveform 18.

When only system trigger pulses 18' are applied to tube 14, the output waveform at anode 16 is substantially an inverted replica of the input signal. This is shown as waveform C of FIG. 2. The time relationships of waveforms A, B and C are shown in FIG. 2.

The circuit of FIG. 1 shows that waveform C is applied to capacitance 36, which acts as a differentiator having a time constant which is of the same order of magnitude as the duration of trigger pulses 18. The resultant waveform obtained from capacitance 36 is shown in FIG. 2 as waveform D, which has negative portions well below its normal level, and small positive pips. As will be hereinafter shown, waveform D is applied to a tube which is normally cut off; the negative portions being below the energizing level of the tube,.and the positive pips having too small an amplitude to energize the tube. It may thus be seen that the trigger pulses alone do not produce an initiating signal.

The action of initiating multivibrator 12 in response to the marker signal may now be considered. Returning again to FIG. 1, when a 10 marker signal is obtained from the rotating antenna, it is of the shape of waveform 40. This waveform is passed through a pulse producing circuit 42, such as a Schmidt trigger circuit. A Schmidt trigger circuit is one which produces a pulse type waveform whose leading edge occurs when the input signal exceeds a given value, and whose trailing edge occurs when the input signal drops below a given value. The output of pulse producing circuit 42 is shown in FIG. 2 as waveform F. This waveform is differentiaetd by capacitance 46 to produce waveform G of FIG. 2. Waveform G is applied to tube 50 which is normally cut off. The negative going spike of waveform G merely drives tube 50 further into cutoff, and therefore produces no output signal. The positive going spike of waveform G causes tube 50 to become conductive, and act as a polarity inverter. The output waveform H from tube 50 therefore contains only a negative going energizing spike 54, which occurs at the instant marker signal 40 exceeds a given level. Waveform H is applied to the second tube 56 of multivibrator 12 through a coupling capacitance which isolates the grid of tube 56 from the potential at the anode of tube 50.

If multivibrator 12 is OE, its normal state, tube 56 is conductive. The negative going spike 54 of waveform H cuts off tube 56, which because of the inherent multivibrator action, turns on tube 14. It may therefore be seen that whenever marker signal 40 exceeds a given level, multivibrator 12 is turned On. It may also be seen that when marker signal 40 decreases its amplitude, there is no effect on multivibrator 12,

The action of multivibrator 12 to this point may be summarized as follows. It may be turned On either by the trigger pulse or the marker signal, but is always turned Off by the next trailing edge of the system trigger.

It will now be advantageous to study the output of initiating multivibrator 12 under the influence of marker signal 40 and trigger pulses 18. Under the combined influence of marker signal 40 and system trigger pulses 18, multivibrator 12 produces waveform C' of FIG. 2. It will be seen that under the combined action of the marker signal and the system trigger, waveform C of FIG. 2 has a series of short duration pulses 58, resulting from the system trigger pulses along, and a longer duration initiating pulse 60, resulting from the turning on action of the marker and turning off action of the system trigger pulses. The leading edge of initiating pulse 60 corresponds to the instant that marker signal 40 exceeded a given level, and the trailing edge of initiating pulse 60 occurs at the subsequent trailing edge of the next system trigger pulse.

The trailing edge of initiating pulse 60 is therefore the time at which an initiating signal should be produced. This is achieved in the following manner.

The output of multivibrator 12 (in this case waveform C of FIG. 2) is applied, as shown in FIG. 1, to capacitance 36. It was previously pointed out that the differentiating circuit comprising capacitance 36 had a time constant which was in the same order of magnitude as the duration of the pulses of waveform C, and therefore produced waveform D of FIG. 2. However, the time constant of this differentiating circuit is short compared to the duration of pulse 60 of waveform C. The differentiation of waveform C produces waveform D wherein the longer duration pulse 60 produces negative going and positive going spikes 62 and 64 shown in FIG. 2. Spike 64 is thus the desired initiating signal.

Waveform D is applied (FIG. 1) to control grid 66 of tube 68 of output multivibrator 10. Tube 68 is normally cut off, and is therefore immune to both the small pips of waveform D', and to the negative going spike 62. When, however, the positive going initiating spike 64 is applied to tube 68, the tube becomes conductive and initiates a positive going intensification pulse 69 at cathode 70.

It may thus be seen that a positive going intensification pulse is produced by output multivibrator 10 at the occurrence of the system trigger which immediately follows the occurrence of a marker signal. More specifically, the intensification pulse is produced by the trailing edge of the trigger signal. It is precisely at this time that a radial spoke like line is started on the presentation, and the leading edge of intensification pulse 69 causes this radial line to become intensified.

It is now necessary to consider how intensification pulse 69 may be terminated. Referring again to FIG. I, it will be seen that system trigger waveform 18 is simultaneously applied to another tube 72 which amplifies and inverts it to form waveform I of FIG. 2. This waveform is applied through capacitance 75, which acts as a blocking capacitance to output multivibrator 10, specifically to the control grid of tube 68. Since tube 68 is normally cut off, the negative going portions of waveform I ordinarily have no effect. If, however, tube 68 were conducting because it had been turned on by the presence of an initiating signal, the negative going portion of waveform I would turn off tube 68. In this way intensification pulse 69, which was originated by marker signal 40, is terminated by the second following system trigger pulse, more specifically by the leading edge thereof. Intensification pulse 69 is of course applied to an element which controls the intensity of the electron beam, and thus the intensity of the radial lines of the display.

The radar display thus has an intensified angle marker line which is originated by the marker signal, but is actually initiated by the trailing edge of the subsequent trigger signal. It is at this instant that a spoke-like line of the presentation is started. This spoke of the display is continued bright by the intensification, which is terminated by the occurrence of the next trigger pulse, which also terminates the spoke-like line. In this way, the angle marker lines produced by my invention are always single lines which start at the center of the presentation, and extend to the periphery thereof.

While I have disclosed the principles and one embodiment of my invention, using a Schmidt trigger, multivibrators, and idiflerentiating circuits to provide energizing spikes therefor, various modifications will occur to those skilled in the art. I desire therefore to be limited only by the following claims.

What is claimed is:

1. In a system having trigger pulses with leading and trailing edges, and a marker signal, the combination comprising: means producing an initiating signal on the occurrence of the trailing edge of the trigger pulse subsequent to the occurrence of said marker signal; means causing said initiating signal to initiate an intensification pulse; and means terminating said intensification pulse on the occurrence of the leading edge of the next subsequent trigger pulse.

2. In a system having trigger pulses with a leading edge and a trailing edge, and a marker signal, the combination comprising: means starting an initiating pulse when said marker signal exceeds a given level; means terminating said initiating pulse on the occurrence of the trailing edge of the subsequent trigger pulse; means causing said initiating pulse to produce an initiating signal; means causing said initiating signal to initiate an intensification pulse; and means terminating said intensification pulse on the occurrence of the leading edge of the next subsequent trigger pulse.

3. In a system containing trigger pulses and a marker signal, the combination comprising: means producing an energizing signal when said marker signal exceeds a given level, said means comprising a Schmidt trigger circuit; means causing said energizing signal to activate a multivibrator; means causing the subsequent trigger pulse to deactivate said multivibrator; means causing said deactivation to produce an initiating signal; means causing said initiating signal to initiate an intensification pulse, said means comprising a second multivibrator; and means causing the next subsequent trigger pulse to terminate said brightening pulse.

4. In combination with a system containing trigger pulses having a leading edge and a trailing edge, and a marker signal, the combination comprising: means producing an energizing signal when said marker signal exceeds a given level, said means comprising a Schmidt trigger circuit; means causing said energizing signal to activate a multivibrator whereby an initiating pulse signal is started; means causing the trailing edge of the subsequent trigger pulse to deactivate said multivibrator whereby said initiating pulse is terminated; means producing an initiating signal which corresponds in time with the termination of said initiating pulse, said means comprising a difierentiating circuit having a time constant which is short compared to the duration of said initiating pulse; means causing said initiating signal to initiate a brightening pulse, said means comprising a connection which applies said initiating signal to a second multivibrator; and means causing the next subsequent trigger pulse to terminate said brightening pulse.

5. In combination with a system having trigger pulses and a marker signal, the combination comprising: means producing an initiating signal on theoccurrence of the trailing edge of the trigger pulse subsequent to the occurrence of said marker signal, said means comprising an initiating circuit; means causing said initiating signal to initiate a brightening pulse, said means comprising means to apply said initiating signal to an output circuit; and means terminating said brightening pulse on the occurrence of the leading edge of the next trigger pulse.

6. The combination of claim 2 wherein said initiating circuit and said output circuits are multivibrators.

7. In combination With a system containing trigger pulses having a leading edge and a trailing edge, and a marker signal, the combination comprising: means to produce an energizing signal when said marker signal exceeds a given level, said means comprising a Schmidt trigger circuit; an initiating multivibrator; means causing said energizing signal to activate said multivibrator whereby an initiating pulse is started, said means comprising a connection from the output of said Schmidt trigger to an input of said multivibrator; means causing the trailing edge of the next subsequent trigger pulse to deactivate said multivibrator whereby said initiating pulse is ended, said means comprising a differentiating circuit connected between the source of said trigger pulses and a second input to said multivibrator, said differentiating circuit having a time constant which is short compared to the duration of said trigger pulses; means to produce an initiating signal which corresponds in time with the ending of said initiating pulse, said means comprising a difierentating circuit having a time constant which is short compared to the duration of said initiating pulse but long compared to the duration of said trigger pulse; means causing said initiating signal to initiate an intensification pulse, said means comprising an output multivibrator and a connection which applies said initiating signal to an input of said output multivibrator; and means causing the leading edge of the next subsequent trigger pulse to terminate said intensification pulse.

8. The combination of claim 7 wherein said last means comprises a connection between said source of trigger pulses and an input to said output multivibrator.

References Cited in the file of this patent UNITED STATES PATENTS 2,719,969 Naidich Oct. 4, 1955 2,764,343 Diener Sept. 25, 1956 2,773,255 Meier et al Dec. 4, 1956 2,802,940 Burton Aug. 13, 1957 2,879,503 Green et al Mar. 24, 1959 2,903,584 Jafiee et a1. Sept. 8, 1959 UNITED STATES EATENT oEEICE CERTIFICATE OF Patent No, 2,989, 703 June 20, 1961 Jerome F. Siegel It is hereby certified that error appears in -the above numbered patentrequiring correction and that the said Letters Patent should read as "corrected below.

Column 3, line 54, for "differentiaetd" read differentiated column 4, line 14, for "along" read ajl'one column 4, line 29 strike out "in"; column 5, line 5, after "intensification" insert pulse Signed and sealed this 16th day of January 1962.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer I I DAVID L. LADD Commissioner of Patents UNITE-D STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,989,703 June 20, 1961 Jerome F. Siegel I It is hereby certified that error appears in ,the above numbered patentrequiring correction and that the said Letters Patent should read as corrected below Y 7 Column 3, line 54, for "differentiaetd" read differentiated column 4, line 14, for "along" read ajl'one column 4, line 29, strike out "in"; column 5, line 5, after "intensification" insert pulse Signed and sealed this 16th day of January 1962.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

